Computer Simulation Analysis of Noise Reduction Effect of Sound Insulation Barrier
Abstract: This paper verifies the actual credibility of computer simulation software in traffic noise control engineering by comparing the traffic noise simulation analysis results of computer simulation software raynoise with the laboratory scale model measurement. Further compare and contrast the different noise reduction effects produced by various forms of road sound barriers, so as to have a deeper understanding of the noise reduction effects of different forms of sound barriers.Keywords: Computer simulation of traffic noise a noise barrier, an overview of the initial stage of China's highway construction, relatively little traffic, no traffic noise attracted attention. With the advent of the automobile era, the rapid increase of highway traffic flow, the city traffic volume has increased sharply, and the urban road traffic noise has become more and more serious to the environmental pollution. It has become one of the public nuisances and has become a hot spot of concern to the world. . Focus on its accuracy and confirm the source of the error. At the same time, software users must be aware that advanced procedures are not a substitute for the user's acoustic knowledge and experience, and that the correctness and accuracy of the input data is another important factor. Through the computer acoustic software, the 3D model is input, and the spatial position of the building, the ground, the terrain, the sound barrier, the sound source, etc. is clearly expressed. Accurately simulate the refraction, reflection, diffraction and absorption of noise propagation between buildings, sound barriers, and terrain through the most detailed description, thereby improving prediction methods and prediction efficiency. II . The basic principle of RAYNOISE software system RAYNOISE is mainly based on geometric acoustics. Geometric acoustics assumes that acoustic waves propagate around the sound in an acoustic environment. When the sound rays collide with a medium or interface (such as a wall), the energy will be lost. In this way, the energy accumulation of sound waves at different positions in the sound field is also different. Since the late 1980s, with the rapid development of computer technology, digital technology is gradually taking the lead. The core of digital technology is to use a multimedia computer to model and program the impulse response. The technology is simple, fast, and the accuracy can be continuously improved, which is unmatched by analog technology. There are two well-known methods for calculating impulse response: virtual source method and sound line tracking method. Both methods have their pros and cons. Later, some methods were combined to combine them, such as the cone beam method and the triangular pyramid beam method. RAYNOISE combines these two methods as the core technology for calculating the acoustic response of the sound field. For the simulation of outdoor traffic noise, the simulation principles on which Raynoise software is based are:1.Softwarediffraction simulationprinciple(1).Diffraction Path The classical geometric analysis method of the sound field (virtual sound source method, vocal line tracking method, hybrid method) does not consider the diffraction of sound. However, since diffraction is important in outdoor traffic noise, RAYNOISE uses an approximation to calculate the diffraction, that is, to calculate the portion of the diffracted wave that reaches the object (the most typical of the barrier). This can be done by searching for the first order diffraction path. This path is the shortest line from the sound source (or virtual source) to the receiving point, and the break point (diffraction point) is on the edge line of the barrier (see Figure 1). Figure 1 S (virtual) sound source, M receiving point, BE diffraction boundary, D diffraction point First, the user needs to define the diffraction boundary in the geometric model, and then RAYNOISE will automatically find the diffraction path that meets the following conditions: 1       The diffraction point is between the two endpoints of the diffraction boundary; 2       The receiving point is in the sound shadow area of ​​the barrier; 3       The first part of the diffraction path (from the sound source to the diffraction point) should not be interrupted by other geometric faces. (2).Accumulation of the diffraction path Naturally, acoustic diffraction often occurs not only in one diffraction path (Figure 2). For example, if a model consists of ground, sound barrier, and receiving points, then three diffraction boundaries will appear (one at the top of the sound barrier and the other two on either side of the sound barrier). Figure 2 A sound barrier has three diffraction boundaries. In this case, it is necessary to calculate the sound pressure contributed by all diffractions to the receiving point, including the phase difference formed by different diffraction paths due to different lengths when the sound source is a continuous sound source. The resulting interference (Figure 3).
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Figure 1 S (virtual) sound source, M receiving point, BE diffraction boundary, D diffraction point First, the user needs to define the diffraction boundary in the geometric model, and then RAYNOISE will automatically find the diffraction path that meets the following conditions: 1       The diffraction point is between the two endpoints of the diffraction boundary; 2       The receiving point is in the sound shadow area of ​​the barrier; 3       The first part of the diffraction path (from the sound source to the diffraction point) should not be interrupted by other geometric faces. ( 2 ). Accumulation of the diffraction path Naturally, acoustic diffraction often occurs not only in one diffraction path (Figure 2). For example, if a model consists of ground, sound barrier, and receiving points, then three diffraction boundaries will appear (one at the top of the sound barrier and the other two on either side of the sound barrier). 
Figure 2 A sound barrier has three diffraction boundaries. In this case, it is necessary to calculate the sound pressure contributed by all diffractions to the receiving point, including the phase difference formed by different diffraction paths due to different lengths when the sound source is a continuous sound source. The resulting interference (Figure 3).